Causes and Countermeasures of the most popular gra

2022-08-05
  • Detail

Causes and Countermeasures of common gravure printing faults (Part 2)

press "input i/4" key II. Poor chromatic accuracy

there are several () reasons for incorrect chromatic registration of plastic film:

(1) change of printing registration in longitudinal direction (running direction)

① change of tension during film traction. Cause: the drum brake of uncoiling device is improperly modulated; Too much roll material or too large diameter of finished roll material; The speed of three rollers is not set properly: the surface friction of the three roller surfaces decreases; Tension variation of rewinder. Countermeasures: check and adjust 1. Name: each control device of microcomputer controlled electro-hydraulic servo horizontal tensile testing machine

② the diameter difference of the plate cylinder is poor. Cause: the increase of diameter difference during plate making is not accurate. Countermeasure: measure the diameter difference

③ abnormal rule line. Cause: insufficient density, printing offset, etc. Countermeasures: adjust the sensitivity of the photocell, and manually eliminate the printing plate paste and other defects

④ the diameter of the plate cylinder is small. Cause: it is difficult to control the overprint accuracy of small roll diameter: the countermeasure is 0.5 ⑴% accuracy: if the printing bag length is short, the mosaic method can be used, that is, more than two bags can be printed on one printing roller

(2) the device is unstable for horizontal alignment to obtain advantages over ordinary metals in strength, toughness, weight, price, etc

causes: ① one side of the film is loose, and the film guide roller is not parallel; ② Uneven printing pressure; ③ Plate cylinder and impression cylinder form taper; ④ The film tension changes, forming the film to swing left and right. Countermeasures: check and adjust each element one by one. If the horizontal alignment device is loose, repair it

III. poor printing fastness

the reasons for poor printing fastness of plastic film are as follows:

(1) poor corona treatment of polyolefin film. Countermeasures: check whether the surface tension of PE and PP reaches above 40 dyne/cm

(2) the internal printing ink has poor affinity with the printed material. This is due to poor proportioning of mixed solvents. Countermeasures: change the ink and adjust the solvent ratio

(3) the temperature and relative humidity of the printing workshop change greatly. Countermeasures: try to control the relative humidity of the workshop between 50% ~ 60%, but not too low. When it is lower than 40%, it is easy to generate static electricity. It is best to control the room temperature at 18 ℃ ~ 23 ℃, and keep the environment clean and ventilated

(4) the printability of the plastic film itself is very poor, and it still does not meet the requirements after corona treatment. Countermeasure: replace the printed materials

IV. pattern size shift

(1) when printing, the longitudinal pattern size shrinks. Cause: insufficient shrinkage allowance. Due to the influence of plastic film tension and heating and drying during printing, the longitudinal dimension of the film is larger than that of the printed text. Countermeasures: when making plates, the size of shrinkage shall be properly reserved, and the film tension shall be kept to the minimum

(2) when printing, the pattern size in the longitudinal direction is extended. Cause: too much shrinkage allowance is left for the printing plate size. Countermeasure: increase film tension

v. poor reproducibility of print level

(1) too deep highlight (bright part). Cause: the printing plate is too deep and contains too much ink. Countermeasures: ① increase the number of target lines; ② Reduce the pigment in the ink; ③ Properly increase the angle between the doctor blade and the plate surface

(2) the highlight is too light. Cause: the printing plate is not deep enough. Countermeasures: ① use dark color ink; ② Properly reduce the angle between the doctor blade and the plate surface

(3) dark tone (dark part) is too deep. Cause: the printing plate is too deep. Countermeasures: due to insufficient ink drying, the ink layer may be caked. If necessary, change the version again

(4) insufficient dark tone density. Cause: insufficient printing plate depth. Countermeasure: use dark tone ink

(5) the depth of the intermediate ink is obvious. Cause: poor inking. Countermeasure: replace the ink with good characteristics

VI. poor dry conjunctiva of post printing ink layer

(1) insufficient hot air temperature, wind speed, air volume and exhaust volume. Countermeasure: adjust the drying device

(2) after printing, the ink layer has the illusion of dry conjunctiva, and there is still residual solvent in the ink layer. After the film is reeled, there is still about 40 ℃ waste heat, which is suitable for the continuous activity of the solvent. In addition, there is a certain pressure during reeling, which causes the harm of back adhesion. Countermeasures: ① the ink layer should be completely dry after printing; ② After printing, the film shall be loosely put in the iron wire basket. After the film is cooled, it shall be reeled, cut and bag made again when there is no back adhesion

Copyright © 2011 JIN SHI